Cherubael

Cherubael is a daemon prince who used to be worshipped on Clanar II and has spent the last few centuries as other people's problem in a box. Quixos bound him. Eisenhorn banished him on Farness Beta, then stuffed him back into flesh because the next fight was worse.

He talks like a courtier and kills like a siege engine. He steered Eisenhorn toward radicalism for a hundred years so the Inquisitor would one day smash the host and set him loose. That plan almost worked.

Godwyn Fischig became the later cage. Cherubael still answers when Eisenhorn is desperate enough to knock. Desperate is a schedule, not a mood.